Pump jack scaffolds are well known. They are temporary structures commonly used to support workmen beside a building structure that requires new construction, repair or maintenance. A pump jack frame comprises only two uprights and relies on the building structure itself for support. A brace is normally extended between each upright and the building structure for such purposes. A jack mechanism encircles each upright, and the pair of jack mechanisms support a work platform. The jack mechanisms are usually pedal-operated to rise on the upright and often have hand-operated cranks that permit lowering. In the past, the uprights have been wood beams, which can be readily gripped by the jack mechanisms. Extruded rectangular aluminum poles are now displacing wood beams. With aluminum poles, a friction material such as wood or rubber is riveted or screwed to one side wall to provide an appropriate gripping surface for a jack mechanism.
There are several shortcomings in current practices relating to pump jack scaffolds with aluminum poles. There is a tendency for the uprights to twist, which contributes to failure of the scaffold. This problem relates to the lack of proper bracing. Another consideration is how to provide adequate bracing between the uprights. Another issue is how to conveniently provide a fall arrestor to ensure worker safety. Yet another problem relates to attachment of the required friction material. Care must be taken to properly recess rivets or screws to avoid interference with the operation of a jack mechanism. Such fasteners have been known to shear, and the friction material has been known to break or pull away from the pole proximate to such fasteners, particularly if rubber is involved. Another problem relates to transportation and general handling. To accommodate two-story buildings, uprights with a length between 20-30 feet are typically required. Such lengths are unwieldy for general transportation. Proposals have been made to provide separable upper and lower sections with an internal bridging joining the two, but lack of torsional rigidity remains a problem. Lastly, it will be desirable in some applications that a pump jack scaffold be made free-standing. Nailing or bolting to a roof to stabilize the pump jack structure may not always be acceptable.
In its various aspects, the invention addresses such shortcomings in prior practices.